Bobs penny bank is 1/5 full. After he adds 500 pennies, it is 7/10 full. How many pennies can Bob's bank hold?

Question

Bobs penny bank is 1/5 full. After he adds 500 pennies, it is 7/10 full. How many pennies can Bob's bank hold?

Answer 1

After adding 500 pennies, the bank rose from 1/5 th full to 7/10 th full.

That means that 500 pennies accounts for the difference ... 7/10 - 1/5

 

    7/10 - 1/5 = 7/10 - 2/10 = 5/10 = 1/2

 

So 500 pennies accounts for 1/2 full bank.

Thus the bank can hold 1000 pennies. 

Answer 2

Think like percentages.  1/5 is 20%.  7/10 is 70%.  He added 50%.  50% is 500 pennies.  So his bank can hold 1000 pennies.